When transporting natural gas in a pipeline hydrates may form in the gas as the temperature of the gas decreases. During hydrate formation crystals are formed which can grow and agglomerate thereby forming hydrate plugs in the gas pipeline which hinder the gas transport thereafter. This problem is generally overcome on the one hand by heating the pipeline and on the other hand by feeding anti-hydrate compounds, typically thermodynamic inhibitors such as methanol, glycol or so called LDHI (Low Dosage Hydrate Inhibitor) type of inhibitors, into the pipeline that inhibit hydrate formation. The disadvantage of heating the pipeline is that it increases the cost of the transport of natural gas substantially. The use of methanol and other type of thermodynamic inhibitors is declining as these are strongly contaminating the environment, and require a substantially higher concentration than the LDHI type of inhibitors. Two types of LDHIs are known: the kinetic inhibitors, which decrease the speed of hydrate formation, and the anti-agglomerate inhibitors, which prevent agglomeration of the hydrate particles. In at least 95% of the cases the companies still employ the conventional, environmentally unfriendly methanol or glycol and expensive heating in order to protect gas pipes from hydrate plugs. Application of the environmentally friendly inhibitors is not yet wide-spread due to the higher expenses, although strong ecological interest is tied to it. The novelty of the present complex invention, in its details and as a whole, ensures the cost efficient and safe employment of inhibitors.
Hereinafter the LDHI type of inhibitors will be discussed, which will simply be referred to as LDHI or inhibitor for the sake of simplicity.
Inhibitors of different type and composition are available of which the selection of the most suitable inhibitor and its feeding rate depends on the various parameters of the gas well, the gas pipeline and the gas to be transported. Such parameters are for example the depth of the gas well, its yield, the natural gas condensate content, the stratum water content, and the carbon-dioxide content of the natural gas, the length and material quality of the pipeline, the flow parameters, the expected temperature conditions within the pipeline, etc. The suitable inhibitor is generally chosen by taking a sample from the gas well-head, transporting the sample to a remote laboratory where different inhibitors are added to the sample and measurements are performed in order to determine the efficiency of the inhibitor. The disadvantage of this method is that the composition of the gas sample and the ratio of the gas phase and liquid phase may change during transportation due to chemical reactions taking place inside the sample. A further disadvantage is that the amount of the sample does not allow for investigating hydrate formation at an industrial scale which may substantially influence the usability of the measurement results.
A great disadvantage of the currently employed inhibitor feeding systems is that regular on-site inspection is required for the continuous control of the reliability of operation. Furthermore, the feeding quantity can only be set on-site as well. In case of possible breakdown of operation or of a change of the environmental conditions (for example temperature) this system can only respond with big delay.
Presently, there is no known, complex, inhibitor feeding system and process using on-site measurements with the help of which the feeding of the rather expensive inhibitor into a gas pipeline could be optimized efficiently. The present solutions do not allow for determining the minimal quantity of inhibitor to be fed in, nor does it allow for early detection of a possible malfunction or breakdown of the feeding system.
It is an objective of the present invention to provide a process which overcomes the problems associated with the prior art. In particular, it is an objective of the invention to provide a process, which allows for the in situ determination of the rate of feeding an inhibitor into a gas pipeline for preventing hydrate formation, as well as remote control of the process of inhibitor feeding, thereby contributing to the spreading of the hydrate prevention technology that is based on the use of inhibitors.